1. Field of the Invention
The present invention relates to a built-in antenna for handheld terminals, and more particularly to a structure of a built-in antenna for handheld terminals configured for efficient use of the internal space of the handheld terminals and for improvement of antenna radiation pattern and efficiency.
2. Description of the Related Art
Handheld terminals such as cellular phones, PDAs, or the like refer to devices enabling users to send and receive data while moving.
There are external antennas as antennas used for the conventional handheld terminals. Such external antennas are placed in an exterior space of a handheld terminal, and classified into mono-pole antennas, helical antennas, and the like.
Such mono-pole antennas are formed of a conductive pole, the antenna length of which is determined based on a frequency domain. Accordingly, such mono-pole antennas have a disadvantage in that the length of the antennas becomes longer than the handheld terminals as the handheld terminals are getting smaller. Further, such mono-pole antennas have a disadvantage of being damaged due to external shocks.
Such helical antennas are formed of a conductive coil wound on a conductive plate. Such helical antennas have an advantage of being structured short compared to the mono-pole antennas, but have a disadvantage of being damaged due to external shocks. Further, since such an external antenna is placed near the head of a user when the user uses a handheld terminal, electromagnetic waves can have adverse influence on the user. In order to eliminate such disadvantages of the external antennas, an inverted-F antenna (IFA) has been proposed.
FIG. 1 is a cross-sectional view for showing a conventional general inverted-F antenna, and FIG. 2 is a perspective view for showing the same. In FIGS. 1 and 2, the inverted-F antenna is configured in a three-dimensional form with a ground part 100, a radiation part 102, a connection part 104, and a power-supply part 106. Hereinafter, description will be made on the inverted-F antenna.
The radiation part 102 is disposed on the upper portion of the ground part 100, and the connection part 104 connects the ground part 100 and the radiation part 102, and is disposed on the end portion of the radiation part 102. The power-supply part 106 provides currents to the radiation part 102. Generally, impedance matching is determined based on the location of the power-supply part 106 and the length, of the connection part 104.
As discussed above, an inverted-F antenna is a built-in antenna so that it can be built in a handheld terminal, thereby considerably solving the disadvantages of an external antenna. In addition, the inverted-F antenna has an advantage of easy production compared with an external antenna.
However, the inverted-F antenna has a problem of having a limitation of maximum compactness and lightness in aspect of the size and the interval between the radiation part and the ground part in light of the trend that the handheld terminals are becoming more compact and lighter. Further, the conventional handheld terminals have a disadvantage of a complicated manufacture and production process due to the structures of the ground part and the power-supply part.